Many display technologies are well known and such technologies are continuing to advance rapidly. For example, modem active matrix display technology can be incorporated into display devices that are relatively lightweight, thin, and which provide high resolution and richly coloured pictures for televisions, computer monitors, and more generally, for a wide variety of display devices that can be incorporated into appliances like personal digital assistants and cellular telephones. While current active matrix displays can be expensive, it is expected that further research will result in advances that will can reduce the costs of such displays and lead to overall greater usage of active matrix display devices.
Active matrix displays are proving to be superior in many ways to older display technologies such as cathode-ray tubes (“CRT”). However, the problem of “glare” off of active matrix displays is also a concern, just as with older CRTs. “Glare” can be defined as ambient light that is reflected off of the device and back towards the viewer, thereby reducing the contrast and overall performance of the display device.
Thus, it is also known to incorporate technology to reduce reflectance into displays and thereby improve their performance. In the case of active matrix displays (or indeed, any other type of pixellated display) it is known to use a black matrix of filtering material. The black matrix is mounted in a complementary fashion to the matrix of pixels in the display, such that the black matrix is a generally continuous filter that surrounds each pixel. Black matrices are described in a number of patents and patent applications, such as “Anti-reflector black matrix for use in display devices and method for preparation of same”, EP 716 334 to Steigerwald (“Steigerwald #1”); “Transmissive Display Device Having Two Reflection Metallic Layers of Differing Reflectances”, U.S. Pat. No. 6,067,131 to Sato (“Sato”); “Anti-reflector black matrix display devices comprising three layers of zinc oxide, molybdenum and zinc oxide”, U.S. Pat. No. 5,570,212 to Steigerwald (“Steigerwald #2”); “Anti-reflector Black Matrix Having Successively A Chromium Oxide Layer, a Molybdenum Layer And a Second Chromium Oxide Layer”, U.S. Pat. No. 5,566,011 to Steigerwald (“Steigerwald #3”); and, “Low Reflectance Shadow Mask”, U.S. Pat. No. 5,808,714 to Rowlands et al. (“Rowlands”). One particular disadvantage to Steigerwald #1, Steigerwald #2 Steigerwald #3 and Rowlands is that they are confined to black matrix structures having specific sets of materials. A more general discussion of applying a black matrix as applied to a display having colour filters is found in U.S. Pat. No. 5,587,818 to Lee (“Lee”).
However, such prior art black matrix structures are not always useful or practical to incorporate into display devices. For example, prior art black matrix structures are frequently formed as a separate unit from the display, thereby eventually requiring the assembly of the black matrix structure to the display structure, such as by mounting the black matrix structure to the front of the display.
It is also known to use optical interference to reduce reflectance in various thin film display technologies, such as electroluminescent devices (“ELD”s). For example, reducing reflectance of ambient light can be achieved by using additional thin film layers sandwiched between one or more layers of the ELD, which are configured to achieve destructive optical interference of the ambient light incident on the display, thereby substantially reducing reflected ambient light. Optical interference technology is discussed in detail in U.S. Pat. No. 5,049,780 to Dobrowolski et al., (“Dobrowolski”) and U.S. Pat. No. 6,411,019 to Hofstra et al. (“Hofstra”). In addition, certain inventors of the present invention have also contemplated the use of the optical interference technology taught in Hofstra and Dobrowolski in conjunction with the bus lines that form the matrix surrounding each pixel in an active matrix display. See Canadian Patent Application 2,364,201 filed Dec. 12, 2001.
More recently, U.S. Pat. No. 6,429,451 to Hung (“Hung”) has proposed another type of ambient light reducing layer also for incorporation into a pixel of the ELD.
However, notwithstanding the improvements provided by the prior art, it is now been discovered that the prior art does not provide ambient light reduction across all areas of the display, as is now offered by polarizers that are also used with prior art displays. Because polarizers can offer substantially uniform ambient light reduction across the entire viewable surface of the display, polarizers can be preferred over other prior art solutions that embed or otherwise incorporate the ambient light reduction means within the actual display structure. In order to obviate the need for polarizers and achieve the attendant advantages eliminating the post production costs associated with polarizers, it is desired to provide a means to substantially uniformly reduce ambient light reflection across the entire viewable surface of the display by means of embedding the contrast enhancement apparatus within the display.